38 RESPIRATION. 



ing and a costal or chest type ; the former is characteristic of men, 

 the latter of women. 



B. In expiration the natural elasticity of the lungs and the chest- 

 wall causes very little muscular action to be needed in natural 

 expiration. In forced expiratory efforts all muscles which depress 

 the ribs may be called into action here. 



What is the force of the respiratory effort ? 



The average man is able to elevate a column of mercury in a 

 manometer tube 2? to 3 inches by an effort at inspiration. In 

 expiration, when forced, the mercury will range about an inch 

 higher, but it should be remembered that many muscles which are 

 ordinarily used for other purposes may be called into play in this 

 effort. 



What is meant by the term " vesicular murmur " ? 



It is the sound heard in listening over a normal lung during 

 respiration, and is described as a soft sighing sound heard at the 

 instant air enters the alveoli. Its cause is not fully understood, 

 but it is supposed to be due to the friction of the air against the 

 walls of the vesicles. 



What is tidal air? 



The amount of air which is habitually changed in an ordinary 

 act of breathing. In forced inspiration the excess of air is known 

 as complemental air. 



What is reserve air? 



The air left in the lung after ordinary expiration. After forced 

 expiration there always remains a certain amount of air, known as 

 residual air. 



What is the respiratory capacity? 



The greatest quantity of air which one can drive from the lungs 

 after forced inspiration : this is about 225 cubic in. in an average 

 adult man. The tidal air for the same man will be about 30 cubic 

 in. These figures are not constant, and vary with conditions of 

 health, figure, age, sex, and atmospheric conditions. 



What is the normal rapidity of the respiration ? 



In a healthy adult 14 to 18 per minute. In infants and invalids 

 the rate is often much more rapid. The ratio to the pulse-rate is 

 about 1 to 5 in the healthy individual. 



